1. Field of the Invention
This invention relates to magnetic disk drives. In particular, embodiments of the present invention relate to disk drives, head stack assemblies and actuator arm assemblies that include a tang supporting surface that includes one or more cleating features that increase the surface area thereof.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a slider with at least one transducer or read/write element for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
FIG. 1 shows an example of a conventional actuator assembly 10. As shown therein, the conventional actuator assembly 10 includes a body portion 12 from which are cantilevered one or more actuator arms 14. Also cantilevered from the actuator body portion 12 is a coil portion that includes first and second actuator fork members 16 and 18. The actuator fork members 16 and 18 support the wound coil 22 that forms a portion of actuator coil portion. The wound coil 22 is also at least partially encased by a plastic overmold 20, which serves to further support and add rigidity to the coil 22 and actuator assembly 10. As shown, the actuator assembly 10 may also include a bobbin 25 that is secured to the wound coil 22 by an adhesive and that increases the rigidity of the coil 22 and that of the actuator assembly 10.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. The slider is said to be “flying” over the disk when in this state.
Understandably, such drives may be relatively sensitive to shocks occasioned by mishandling, excessive vibrations, drops and other events causing a rapid acceleration of the disk drive. Indeed, should the head crash into a spinning disk because of a rotational shock, for example, the high stiction (a contraction of the phrase “static friction”) of the disk may prevent the disk from spinning and developing the laminar airflow necessary for the head to lift away from the disk. This problem is particularly acute when the disk includes an outermost layer of glass. As the glass surface is highly polished, there is then a great amount of contact surface area between the head and the disk, increasing the friction therebetween. Should the head contact the disk, it may then literally stick thereto, potentially ruining the entire drive.
In an effort to mitigate the effects of such shocks (e.g., rapid accelerations), a number of latches have been developed to latch the HSA and prevent the head(s) from contacting the disk(s). The operative mechanism of such latches may be mechanical, electromechanical or magnetic in nature. The first function of a latch is typically to limit the travel of the HSA both toward the inner diameter (hereafter “ID”) and toward the outer diameter of the disk. The second function typically discharged by such latches is to prevent the heads of the HSA from leaving the ramp load (if a ramp load is present) or a landing zone on the disk (if a landing zone is present around, for example, the ID of the disk) during shock events that might otherwise jolt the heads from the ramp or landing zone and onto the data-carrying portion of the disk during non-operative conditions of the drive.
Electromechanical and magnetic latches conventionally rely on a metallic tang or similar structure (shown at reference numeral 24 in FIG. 1) protruding from the overmolded voice coil portion or attached to an actuator fork member of the HSA. Either a permanent magnet or an electromagnet is then typically used to attract the tang 24 and to latch the HSA when the drive is not in operation. To ensure that adequate shock protection (especially in small form factor drives suitable for mobile computing applications), the latching force (the force with which the latch holds the tang to the permanent or electro-magnet) must be great. In the case of a permanent magnet, however, a high magnitude latching force requires a correspondingly great de-latching force to free the tang from the attractive force of the magnet. Such de-latching force is typically achieved by so-called resonance de-latching, wherein alternating current is applied to the voice coil portion of the HSA at a predetermined resonant frequency to cause the HSA to break free of the attractive force of the permanent magnet. The stronger the magnet, however, the greater the current is necessary to de-latch the HSA when the drive is called into active operation. Such high latching and de-latching forces place a great strain on the interface between the surface of the actuator assembly that supports the tang and the tang. FIG. 1A shows a top view of the tang and the tang 24 and the tang supporting surface (which may be a portion of the fork member 16 or 18). As shown, the tang-supporting surface 27 conventionally is smooth and flat over its entire surface. Between the tang 24 and the tang-supporting surface 27 is a layer of adhesive 26. The structure of such interfaces is not believed to be optimal in view of the large latching and de-latching forces occurring in the latch assemblies of conventional disk drives. From the foregoing, therefore, it may be appreciated that strengthening the bond between the tang-supporting surface of the actuator assembly and the tang is desirable.